1. Field of the Invention
This invention relates to a rubber composition, a hose of low fuel permeation, and an electroconductive hose of low fuel permeation. More particularly, it relates to a rubber composition of good fuel impermeability and low-temperature flexibility, and a hose of low fuel permeation utilizing this rubber composition, and also to a rubber composition of good fuel impermeability, low-temperature flexibility and electroconductivity, and an electroconductive hose of low fuel permeation utilizing this rubber composition.
2. Description of the Related Art
Control on the leakage of fuel by permeation from an automobile, which is similar to the SHED control (Shield Housing for Evaporative Determinations) in the United States, is put into practice in Japan and Europe in 2000 A.D. A fuel transporting hose is required to be highly impermeable to fuel, since it is greatly responsible for the leakage of fuel by permeation from an automobile, as is well known.
In Japan and Europe, NBR (acrylonitrile-butadiene rubber) or blend rubber of NBR and PVC (polyvinyl chloride) of general specifications is used for a fuel hose in an automobile, such as a filler, breather or evaporation hose. However, that type of hose fails to achieve any fuel impermeability conforming to the strengthened domestic control as stated above. In addition, the rubber material noted above often releases a plasticizer, a vulcanizing agent or its reaction product, when dipped in fuel. In particular, the vulcanizing agent or its reaction product, if released, will corrode the metallic members of a fuel pump or will clog the valves in fuel piping.
In the United States in which the SHED control is already in force, FKM (fluororubber) or resin is used for the inner layer of a hose, and NBR-PVC (blend rubber of NBR and PVC), ECO (epichlorohydrin rubber), CSM (chlorosulfonated polyethylene rubber), etc. for its outer layer. These United States specifications can be expected to achieve the fuel impermeability conforming to the control. There are, however, problems, since FKM and fluororesins are expensive, and the inner layer of FKM or resin is difficult to bond to the outer layer.
It has heretofore been said that increasing the AN content (combined acrylonitrile content) of NBR in NBR-PVC to a range falling between 36 and 42% by weight or so could improve the fuel swelling resistance of NBR-PVC. The inventors of this invention, however, have found that the fuel impermeability of NBR-PVC in which the AN content of NBR falls within that range is still poor.
The inventors have further found that increasing the AN content of NBR to a range falling between 43 to 50% by weight or so realizes good fuel impermeability of NBR which is comparable to that of FKM.
However, increasing the AN content thereof to such a high level will decrease the low-temperature properties of the rubber material necessary to fuel hoses (for example, the flexibility of hoses used in cold districts where the ambient temperature often reaches -30.degree. C. or so). To improve the low-temperature properties of rubber materials for hoses, in general, the amount of the plasticizer to be added thereto will be increased, which, however, adversely affects the fuel impermeability of the hoses formed of such rubber materials.
Apart from the problems of fuel impermeability and low-temperature flexibility of hoses noted above, it is also advantageous to make fuel hoses have electroconductivity. While an automobile is driven or refueled, fuel flows in the fuel hose to generate static electricity. If kept charged with static electricity, the fuel hose will give sparks dangerous to fuel when it is contacted with a metallic refueling gun or the like. To avoid the dangerous trouble, for example, an earth wire may be disposed between a filler hose and the body of an automobile thereby to remove static electricity through it, which, however, requires some specific members and an additional step for fitting it. It will be rather reasonable to use a filler or breather hose having electroconductivity. However, FKM and fluororesins essentially have large electric resistance, and hoses having the inner layer formed of these materials could hardly have electroconductivity.